1. Field of the Invention
The invention relates to concrete finishing trowels which employ one or more rotatable blade-equipped rotor assemblies for finishing a concrete surface. More particularly, the invention relates to a concrete finishing trowel, such as a riding trowel, having rotor assemblies that can be tilted for a steering operation.
2. Description of the Related Art
A variety of machines are available for smoothing or otherwise finishing wet concrete. These machines range from simple hand trowels, to walk-behind finishing trowels, to self-propelled finishing trowels including some larger walk-behind machines as well as relatively large two-rotor or even three-rotor machines. Self-propelled finishing trowels, and particularly riding finishing trowels, can finish large sections of concrete more rapidly and efficiently than manually pushed finishing trowels. The invention is directed to self-propelled finishing trowels and is described primarily in conjunction with riding finishing trowels by way of explanation.
Riding concrete finishing trowels typically include a mobile frame including a deck. At least two, and sometimes three or more, rotor assemblies are mounted on an underside of the deck. Each rotor assembly includes a driven shaft extending downwardly from the deck and a plurality of trowel blades mounted on and extending radially outwardly from the bottom end of the driven shaft and supported on the surface to be finished. The driven shafts of the rotor assemblies are driven by one or more self-contained engines mounted on the frame and typically linked to the driven shafts by gearboxes of the respective rotor assemblies. The weight of the finishing trowel and the operator is transmitted frictionally to the concrete by the rotating blades, thereby smoothing the concrete surface. The individual blades usually can be tilted relative to their supports, via operation of a suitable mechanical lever and linkage system accessible by an operator seated on an operator""s platform to alter the pitch of the blades, and thereby to alter the pressure applied to the surface to be finished by the weight of the machine. This blade pitch adjustment permits the finishing characteristics of the machine to be adjusted. For instance, in an ideal finishing operation, the operator first performs an initial xe2x80x9cfloatingxe2x80x9d operation in which the blades are operated at low speeds (on the order of about 30 rpm) but at high torque. Then, the concrete is allowed to cure for another 15 minutes to one-half hour, and the machine is operated at progressively increasing speeds and progressively increasing blade pitches up to the performance of a finishing or xe2x80x9cburningxe2x80x9d operation at the highest possible speedxe2x80x94preferably above about 150 rpm and up to about 200 rpm.
The blades of riding trowels can also be tilted, independently of pitch control for finishing purposes, for steering purposes. By tilting the driven shafts of the rotor assemblies, the operator can cause the forces imposed on the concrete surface by the rotating blades to propel the vehicle in a direction extending perpendicularly to the direction of driven shaft tilt. Specifically, tilting at least the driven shaft of the rotor assembly from side-to-side and fore-and-aft steers the vehicle in the forward/reverse and the left/right directions, respectively. It has been discovered that, in the case of a riding trowel having two rotor assemblies, the driven shafts of both rotor assemblies should be tilted for forward/reverse steering control, whereas only the driven shaft of one of the rotor assemblies needs to be tilted for left/right steering control.
The most common steering assemblies are mechanically operated. These assemblies typically include two steering control levers mounted adjacent the operator""s seat and accessible by the operator""s left and right hands, respectively. Each lever is mechanically coupled, via a suitable mechanical linkage assembly, to a pivoting gearbox of an associated rotor assembly. The operator steers the vehicle by tilting the levers fore-and-aft and side-to-side to tilt the gearboxes side-to-side and fore-and-aft, respectively. Steering assemblies of this type are disclosed, e.g., in U.S. Pat. No. 4,046,484 to Holz and U.S. Pat. No. 5,108,220 to Allen et al.
Mechanically operated steering control assemblies of the type disclosed in the Holz and Allen et al. patents are difficult to operate because they require the imposition of a significant physical force by the operator. The typical steering control lever requires 20-40 pounds of force to operate in either its fore-and-aft direction or its side-to-side direction. Most operators experience fatigue when exerting these forces, particularly when one considers that the operator must exert these forces continuously or nearly continuously for several hours at a time with little or no rest. Operator fatigue is particularly problematic with respect to side-to-side motions, which, due to the ergonomics of the machines, are considerably more difficult for operators to impose than fore-and-aft motions.
Proposals have been made to replace the traditional mechanically operated steering control assemblies of a concrete finishing machine with power-actuated assemblies. For instance, Whiteman Industries, Inc., of Carson, California has introduced a hydraulically steered riding trowel under its tradename xe2x80x9cHTS-Series.xe2x80x9d This machine is hydrostatically driven via hydrostatic pumps which are powered by the machine""s engine and which supply pressurized hydraulic fluid both to hydraulic motors of the rotor assemblies, and to hydraulic steering cylinders which tilt the driven shafts of the rotor assemblies. The steering assemblies are controlled by joysticks mounted on the operator""s platform adjacent the operator""s seat. These joysticks are easier to operate than traditional mechanical levers. The operator therefore does not experience the fatigue experienced by operators of traditional, mechanically steered machines.
A hydrostatically steered concrete finishing trowel, though superior in some respects to a mechanically steered machine, exhibits its own drawbacks and disadvantages. For instance, the hydrostatic pump, hydraulic motor, steering cylinders, and associated hydraulic devices render the machine very heavy. Accordingly, even with the blades set at their minimum pitch so as to distribute the machine""s weight over a maximum area, the operator must let the concrete set longer than otherwise would be necessary before he or she can perform the initial, so-called xe2x80x9cfloatingxe2x80x9d finishing operation. This delay hinders a finishing operation because it leaves the operator with less time to finish the concrete. In addition, the complex hydraulic system required by hydrostatically steered machines is prone to leaks. Oil spills on fresh concrete are, of course, undesirable. Finally, hydrostatically steered machines are considerably more expensive than manually-steered machines due to the relatively large and expensive hydraulic motors, valves, etc.
A need therefore has arisen to provide a self-propelled finishing trowel having a steering control assembly that can be operated automatically and that is relatively lightweight, inexpensive, and reliable when compared to mechanically steered machines and hydrostatically steered machines.
It is therefore a first principal object of the present invention to provide a self-propelled finishing trowel that incorporates a power-actuated steering system that is relatively simple, lightweight, and inexpensive.
Another object of the invention is to provide a self-propelled concrete finishing trowel that meets the first principal object and that substantially eliminates or at least significantly reduces operator fatigue.
Yet another object of the invention is to provide a concrete finishing trowel that meets the first principal object and that does not require high pressure fluids for its operation and, hence, exhibits reduced possibility of hydraulic fluid spills when compared to systems requiring high pressure fluids for their operation.
A second principal object of the invention is to provide an improved method of steering a self-propelled concrete finishing trowel that requires the imposition of only small actuating force by the operator and, accordingly, is not fatiguing to the operator.
Another object of the invention is to provide a method that meets the second principal object and that does not utilize heavy, complex, and leak-prone hydraulic systems.
In accordance with a first aspect of the invention, these objects are achieved by steering a concrete finishing trowel not with a mechanical lever system or a hydraulic system, but with electronic actuators such as ball screw actuators. The actuators are controlled indirectly by way of a controller such as an electronic joystick and, when energized, tilt at least the driven shaft(s) of the machine""s rotor assembly or rotor assemblies to effect the desired steering operation.
Preferably, the actuator or actuators of the actuator arrangement associated with each rotor assembly is/are connected to that rotor assembly by a relatively simple steering linkage connected directly to the rotor assembly""s gearbox. In the typical case of a riding trowel having two rotor assemblies, two actuators and a biaxially pivoting steering linkage will be supplied for one of the rotor assemblies to effect both left/right and forward/reverse steering control, whereas only a single actuator and its associated uniaxially pivoting steering linkage will be provided for the other rotor assembly so as to effect only forward/reverse steering control.
The controller may comprise any structure converting physical movement of the operator into an electronic steering command signal. For instance, it may comprise one or more joysticks, preferably a proportional control joystick, that is electronically coupled to the actuators. The joystick(s) is/are coupled to the actuators such that, as the actuators move, a feedback circuit compares the joystick position with the actuator position and continues actuator energization until the actuator position matches the commanded position as determined by the joystick position. If the joystick is released, the actuator returns automatically to its centered position. Due to the nature of the feedback circuit between the joystick and the respective actuator, the travel speed of the machine over the surface to be finished is directly proportional to the magnitude of joystick movement, and the machine moves in the direction of the joystick movement. Because the operator input forces are very small, operator fatigue is significantly reduced during operation of the invention when compared to operation of traditional, mechanically steered machines.
These and other objects, advantages, and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.